This invention relates to a white balance controlling apparatus, method and program for controlling the adjustment amount for a color signal for the adjustment of the white balance and image pickup apparatus thereof.
In recent years, an image pickup apparatus such as a digital still camera, a digital video camera and so forth for which a solid-state image pickup device is used has been and is being popularized rapidly. In such an image pickup apparatus as just mentioned, various digital signal processes for correcting the picture quality are performed for a signal obtained by image pickup. As a representative one of image quality correction functions, a white balance adjustment function is known. The white balance adjustment function is a function for adjusting the hue so that a white color is displayed property in response to the color temperature of an image pickup light source for a subject. Also an image pickup apparatus is used frequently which includes an automatic white balance function for detecting the color temperature of an image pickup light source using a signal of a picked up image or an external detector to automatically adjust the hue. Generally, according to the automatic white balance function, a gain is applied to each of RGB signals in a signal of a picked up image so that red, green and blue are equal in ratio to each other at a white color point to be used as a reference in the picked up image.
Incidentally, a green subject such as a leaf under a light source of the sun and a white subject such as a piece of tableware under a light source of a fluorescent lighting have spectral characteristics substantially same as each other. Therefore, where RGB signals in a signal of a picked up image are separated by a color filter, the RGB signals appear as signals substantially same as each other, and discrimination of the signals is difficult. Therefore, there is a problem to be solved that green under a light source of the sun is decided as white in error under a light source of a fluorescent lighting and a white balance adjustment process suitable for a light source of a fluorescent lighting is performed for the green. Further, there is another problem that, conversely, white under a light source of a fluorescent lighting is decided as green in error under a light source of the sun and a white balance adjustment process suitable for a light source of the sun is performed for the white.
In order to solve the problems, a technique has been proposed wherein the number of color filters is increased to detect an emission line unique to a light source of a fluorescent lighting to discriminate whether a subject is a green subject which is under a light source of the sun or a white subject which is under a light source of a fluorescent lighting. The technique is disclosed, for example, in Japanese Patent Laid-Open No. 2003-259380.
However, according to the technique disclosed in Japanese Patent Laid-Open No. 2003-259380, since it includes a new color filter provided additionally, the structure of an image pickup device and the configuration of a processing circuit for an image pickup signal must be altered. Therefore, the production cost increases.
It is desired to provide a white balance controlling apparatus which can enhance the quality of images to be obtained by image pickup of a green subject under a light source of the sun and a white subject under a light source of a fluorescent lighting without the requirement for additional provision of a new color filter.